Five hundred Councilors served on the βουλή for the year, but practical concerns required that they be divided into smaller groups. Accordingly, the legislative year was divided into ten parts, each called a “prytany” (πρυτανεία); for each prytany, the fifty Councilors (βουλεῦται) from one of the ten tribes (φυλαί) served as “presidents,” or prytanes (πρυτάνεις, in the singular, πρύτανις) (Aristot. Ath. Pol. 43.2-3; the inscription Agora 15.38 contains a list of tribes and when they held the prytany). The first four prytanies were 36 days long, the last six were 35 days long, “for the year is divided into lunar months” (Aristot. Ath. Pol. 43.2).

The order in which the Councilors from each tribe served as presidents was random, determined by lot (Aristot. Ath. Pol. 43.2). The random determination seems to have taken place at the end of each prytany (rather than all at once at the beginning of the year), so no one could predict which tribe would serve next. An inscription makes reference to “the presidents, whichever ones might hold that position after the tribe of Oineis” (τοὺςπρυτάνειςοἳἂντυγχάνωσιπρυτανεύοντεςμετὰτὴνΟἰνηΐδαφυλὴν) (IG II2 553.16-17). When the decree was written, the Councilors from the tribe of Oineis were serving as prytanes, or presidents; the decree needed to refer to the next group of presidents, but that group was clearly not known. So, we can infer from this that the selection must have happened toward the end of a prytany. Obviously, during the ninth prytany of the year, it would be obvious that whichever tribe had not yet served would hold the presidency for the final prytany.

This elaborate randomization of the presidency was probably intended to limit possibilities for corruption. No one could plan to introduce business to the Council when a particular tribe held the presidency, and no Councilor could know in advance when he would serve as a president.

The presidents ate their meals together in the Tholos, the “Round House.” They planned and organized meetings of the Council and posted an agenda for each meeting beforehand (Aristot. Ath. Pol. 43.3; meetings of the Council are discussed below).

Aristotle tells us that “There is a chairman of the presidents, one man, chosen by lot; this man chairs for a night and a day—no longer—and cannot become chairman a second time” (ἔστιδ’ἐπιστάτηςτῶνπρυτάνεωνεἷςὁλαχών.οὗτοςδ᾽ἐπιστατεῖνύκτακαὶἡμέραν,καὶοὐκἔστινοὔτεπλείωχρόνονοὔτεδὶςτὸναὐτὸνγενέσθαι) (Aristot. Ath. Pol. 44.1). This chairman kept the keys to the treasuries and archives of Athens, as well as the state seal (τὴνδημοσίανσφραγῖδα) (Aristot. Ath. Pol. 44.1).

In addition to a daily meeting of all the presidents, the chairman and one third of the presidents were required to be on hand in the Tholos constantly (Aristot. Ath. Pol. 44.1); presumably only the chairman was on duty for a full 24 hours, and the other presidents could divide the day into 8 hour shifts. These men, on-call in the Tholos, represented the whole government of Athens in a time of crisis, at least until the full Council or Assembly could be convened. Heralds and envoys from other states came to the presidents in the Tholos first, as did messenger bearing official letters (Aristot. Ath. Pol. 43.6).

Demosthenes describes a dramatic scene, that shows clearly the function of the presidents and the chairman. In 339 BCE, Philip of Macedon marched his army south and captured the city of Elatea, thus threatening Thebes and the Thebans’ southern neighbor, Athens (source for date: Raphael Sealey, Demosthenes and his Time: a study in defeat [Oxford, 1993] 195). Demosthenes describes what happened when news of this threat came to Athens:

“Evening had already fallen when a messenger arrived bringing to the presiding councillors (πρυτάνεις) the news that Elatea had been taken. They were sitting at supper, but they instantly rose from table, cleared the booths in the marketplace of their occupants, and unfolded the hurdles, while others summoned the commanders and ordered the attendance of the trumpeter. The commotion spread through the whole city. At daybreak on the next day the presidents summoned the Council to the Council House, and the citizens flocked to the place of assembly. Before the Council could introduce the business and prepare the agenda, the whole body of citizens had taken their places on the hill. The Council arrived; the presiding Councilors formally reported the intelligence they had received; and the courier was introduced” (Dem.18.169-170).

So, in a crisis, the safety of Athens lay first in the hands of the presidents and the chairman. It is worth noting that because there were 354 days in the legislative year (Aristot. Ath. Pol. 43.2), more than two thirds of all Councilors would serve as chairman for a night and a day in a given year.

There are further implications, if we accept the estimate of two scholars that in 400 BCE there were approximately 22,000 adult male citizens—it is beyond the scope of this article to give evidence and justification for this, but the arguments are presented in Victor Ehrenberg, The Greek State, 2nd English Edition (Methuen, 1969) 31, whose estimate is 20,000-25,000, and in A.W. Gomme, The Population of Athens in the Fifth and Fourth Centuries B.C. (Blackwell, 1933) 26, whose estimate is 22,000.

A citizen had to be 30 years old to serve as a Councilor (Xen. Mem. 1.2.35). For the sake of argument, we might assume that the average citizen would then have an active political life of 30 years, until he was 60. During that time, there would need to be approximately 10,000 chairmen, each controlling the state seal and the treasuries, and presiding over the presidents of the Council for a day and a night (Aristot. Ath. Pol. 44.1). Since no one could serve as chairman twice (Aristot. Ath. Pol. 44.1), this office would have to go to 10,000 different Athenians. It follows, then, that approximately one half of all Athenian citizens would, at some point during their lives, have the privilege and responsibility of holding this office, arguably the closest equivalent to a Chief Executive in the Athenian democracy.